The invention relates to a circuit arrangement for generating a line frequency sawtooth deflection current having a trace period and retrace period through a deflection coil, said arrangement including a first sawtooth network comprising a first diode, said deflection coil, a trace capacitor and a retrace capacitor, a second sawtooth network comprising a second diode, a second coil, a second trace capacitor and a second retrace capacitor, the retrace period for the current when flowing through the second coil being approximately equal to the retrace period for the deflection coil, the arrangement also including supply terminals for receiving a supply voltage from a source and a controlled switching arrangement which is non-conducting during the retrace period, said sawtooth networks being connected together such that the first and second diodes are connected in series with the same conductivity direction, the series arrangement of the diodes being coupled to the controlled switching arrangement, and control means for varying the voltage across one of the trace capacitors.
Such an arrangement is disclosed in United Kingdom Patent Specification No. 1 459 922, the arrangement principally being used to correct for East-West pin-cushion distortion in television displays where the control means causes a parabolic voltage variation at field rate to be present across one of the trace capacitors, in practice the second trace capacitor. This mentioned Patent Specification also contemplates further corrections being applied to the circuit arrangement, such as for changes in the supply voltage, these further corrections being at a relatively low rate compared with the line frequency and being effective across a third trace capacitor in a third sawtooth network. It has been found that if it is desired to insert an information or correction signal having a rate of the order of the line frequency into the circuit arrangement this cannot readily be achieved by the above arrangement, even if modified with a third sawtooth network as this higher frequency signal would either be impeded by the reactance of the relevant coil while if it were not so impeded it would not produce the desire reaction during the line period in which it is applied owing to the action of the relevant clamping diode.